MIMO - Computer Definition

A technique for increasing wireless bandwidth by spatial antenna diversity, MIMO is incorporated into IEEE 802.11n specifications for wireless LAN (WLAN) and 802.16 specifications for broadband wireless access (BWA), more commonly known as WiMAX. As radio signals travel from transmitter to receiver in an enclosed space, they propagate along multiple paths. The signal elements traveling a direct path along a line of sight (LOS) arrive first and strongest.Those that travel the least direct paths, having reflected off walls, floors, ceiling, potted plants, people, and other obstructions, not only arrive last, but also suffer the greatest attenuation due to absorption, diffusion, and other contributing factors. MIMO technology employs multiple spatially diverse transmit antennas to actually encourage the signals to traverse multiple paths and multiple receive antennas to extract additional information from the signals that do so. MIMO algorithms in the receive device correlate and recombine the signals, realizing diversity gain, i.e., an increase in signal strength, in the process. MIMO technology doubles the spectral efficiency.The 802.11n MIMO technology, for example, is expected to yield a theoretical maximum signaling rate of 108 Mbps, compared to the 54 Mbps yielded by the earlier 802.11g technology. See also 802.11g, 802.11n, 802.16, absorption, attenuation, bandwidth, BWA, diffusion, gain, IEEE, LOS, spatial diversity, spectral efficiency, WiMAX, and WLAN.

This "Pre-N" wireless router from Belkin uses two transmitters and three receivers to provide 108 Mbps between its access point and Belkin Pre-N cards in laptops. Introduced in 2004, this was the first "Preliminary-802.11n" system on the market (see 802.11n). (Image courtesy of Belkin Corporation, www.belkin.com)